%%
%% The LaTeX Companion, 3ed
%%
%% Example 10-9-2 on page II-94 in "Latin Modern Typewriter".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{223.0pt}

  \usepackage{lmodern}
  \usepackage[proportional,light]{zlmtt}
  \renewcommand{\monott}[1]{{\def\ttdefault{zlmtt}\texttt{#1}}}  % suggested fixes
  \renewcommand{\proptt}[1]{{\def\ttdefault{zlmvtt}\texttt{#1}}}

  \raggedright

%StartShownPreambleCommands
\usepackage{lmodern}
\usepackage[proportional,light]{zlmtt}
\newcommand\allletters{The dazed brown fox
 \textit{quickly} gave 12--3 \textbf{jumps}!}
%StopShownPreambleCommands

\begin{document}
\texttt{\allletters} (proportional)  \par
\proptt{\allletters} (no change)     \par
\monott{\allletters} (monospaced)    \par
\lctt  {\allletters} (light cond.)   \par
\itshape
\lctt  {\allletters} (+italic \dots) \par
\texttt{\allletters}                 \par
\end{document}
